Method of making pentaerythritol dehydration products



Patented Apr. 26, 1949 METHOD OF MAKING PENTAERYTHRITOL DEHYDRATION PRODUCTS Joseph A. Wyler, Allentown, Pa., assignor to Trojan Powder Company, a corporation of New York No Drawing. Application January 10, 1948, Serial No. L675 Claims. (Cl. 260-338) This invention relates to the dehydration of pentaerythritols.

In my copending application Serial No. 665,321, filed April 26, 1946, now Patent No. 2,462,047, issued February 15, 1949, I have described heating pentaerythritol with sulfuric or like acid. This heating causes the partial dehydration of the pentaerythritol and at the same time poly merization. The polymerization in fact proceeds so far in cases of vigorous action of the acid that, when the product is later esterified with a fatty drying oil such as talloil in making varnish esters, objectionable jelled masses or fish eyes appear.

With the use of a strong acid in this reaction, the dehydration and polymerization occur simultaneously. As compared to the efiect of a Weaker acid such as phosphoric, sulfuric acid being stronger produces in a given time more extensive dehydration and a correspondingly larger degree of polymerization.

Contrary to the general rule that dehydration and polymerization in this reaction go hand in hand and one is greater when the other is also greater, my new method described herein produces the desired dehydrating effect while decreasing the extent of the polymerization. I have discovered that heating the selected pentaerythritol with an aromatic sulfonic acid, preferably mixed with phosphoric acid and under the conditions described herein, gives a more rapid dehydrating efiect than even the strong sulfuric acid and at the same time less polymerization.

The present invention comprises the method of dehydration of pentaerythritol while minimizing polymerization thereof by heating the pentaerythritol With the aromatic sulfonic acid.'

In one embodiment the invention comprises the addition to the sulfonic acid of one of the oxy acids of phosphorus.

As the pentaerythritol selected as the starting material, there is used pentaerythritol itself or the dior tripentaerythritol. Mixtures of these materials also may be employed.

As the sulfonic acid there is used one of the sulfonic acids of the lower benzene hydrocarbons, that is, of the monocyclic aromatic hydrocarbons. Toluene sulfonic acid is the preferred acid. Others that may be used are benzene sulfonic acid and xylene sulfonic acid.

The oxy acid of phosphorus that is used in one embodiment of the invention is preferably phosphoric acid. Phosphorous acid or metaphosphoric acid may be used but their use is not recommended over that of the more readily available phosphoric acid, the so-called ortho phosphoric.

As to the proportions of the raw materials to each other, these may be varied within wide limits. Of the sulfonic acid I use ordinarily 0.1 to 5 parts for parts of the selected pentaerythritol. In ordinary commercial operations I use about 0.1 to 1 part of the sulfonic acid.

Proportions here and elsewhere herein unless specifically stated to the contrary are expressed as parts by weight.

The oxy acid of phosphorus, when used, is incorporated in the proportion of about 0.1 to 1 part although the proportion may go as high as 5 parts.

Ordinarily the proportion of the acid used is made higher the more severe the dehydration that is to be efiected or the less severe the condition of treatment as to temperature and time for a given degree of dehydration required.

The reaction is ordinarily carried on at atmospheric pressure and under an atmosphere of ordinary air. Pressures above or below atmospheric may however be used. A stream of inert gas such as carbon dioxide or nitrogen may also be passed through the reaction mixture to carry oiT the Water liberated in the dehydration reaction.

The temperature of the reaction in which the selected pentaerythritol is dehydrated in contact with the acidic agent is at least as high as the temperature at Which Water as liberated from the reaction boils out of the mixture. The temperature on the other hand should not be so high as to cause formation of objectionable amounts of by-products. Suitable temperatures are up to 260 or 270 C. For commercial operations I obtain best results in dehydration with a minimum of objectionable polymerization when temperature of heating of the selected pentaerythritol with the acid dehydrating agent is about 215 to 250 C.

The period of heating at the temperature chosen for the reaction is determined by removing specimens from the batch and determining when the degree of dehydration has progressed to the extent desired in the finished product. This involves determination of the remaining hydroxyl content of the heated mixture by a standard method. Once this period of time has been determined for a given set of conditions in the reaction including proportion of the acid and temperature, then other batches may be heated for the predetermined period and the heating discontinued without waiting for the analysis for hydroxyl content to be completed.

The product of the reaction after cooling is a solid. The solid so made is preferably ground to a fine powder and washed with a small amount of a liquid such as cold Water or alcohol, the washing liquid being removed as far as possible by filtration or centrifuging. The purpose of this washing is to remove most of the free acid or other readily soluble impurities such as soluble mineral salts. A slight improvement in color usually results also from this washing with a small proportion of the water, alcohol or like material. Ordinarily the product is made to contain about 25% to 40% of hydrox yl group thisproportion being realized by control of the time of heating and other conditions in the reaction as described above.

For the products to be used -'witlri'talloil and other drying oil acids in making varnish esters I ordinarily discontinue the heating When the hydroxyl content is found to be 2'7 to 33% of the finished dehydrated pentaerythritol.

It is considered that the mechanism of myreaction is first dehydration of two adjacent hydroxyl groups to form an ether group and the subsequent reaction of the 'hydroxy ether thus formed with additional molecules of the selected pentaerythritol. Whenthe selected pentaerythritol is the monomer a series of reactions which are considered to represent the changes which'I produce are illustrated by the following chemical equations:

QH GHa H HO'OH /CH2\ HOOHZ oHloH "noon, 0Hz

followed by polymerization to Room OHz0 611201120 -OHZ CH OH l: 1

noon; CH2

199.6 parts of pentaerythrit-ol, C(CI-IzO-HM, of M. 'P. 252C. were placed in a suitable heating vessel provided with mechanical stirring, treated with 0.4 part of p-toluenesulfonic acid, and the mixture heated and stirred, to-obtain a uniform mixture. The latter was heated to-235 C. where themixture boiled vigorously, with the evolution of water. After minutes at this temperature, the molten mass was run into pans to solidify.

The product, upon cooling, was only slightly colored. Upon pulverization and analysis, it was found to contain 31.26% OI-I as against 49.50% 0H for the pen taery-thritol used.

The water liberated was slightly in excess of 9% of the weight of the pentaerythritol used.

When this product was used inya tall-oil-rosinlinseed oil esterification reaction under carefully controlled. standard conditions the time required for this esterification mixture to body to an E (125 C. P. S.) viscosityf'or 2.550% solution of the ester in mineral spirits was 6'hours,-wherea-sthe original pentaerythritol' itself'required 18-20 hours to reach an E viscosity.

Example 2 Using a mixture of pentaerythritol and toldenesulfonic acid identical with that of Example 1, but carrying out theheating until a temperature of 248 C. was reached, a total of 11% of water was driven off. This required 15 minutes after the beginning of water evolution. The product contained "32.10% OH and produced, under standard-conditions with the esterification mixture of Example 1, an E viscosity resin in 5 hours. It .willnoted that increasing the temperature improved =the bodying property of the product.

Example 3 Carrying out an experiment in a manner identical with Example 2 except that the reaction batch was held at 248 C. until 13% of water had been driven off, I obtained raproduct which .contained 27.90% OH and produced an E viscosity resin, under the standard conditions, in.4 /2-1101115.

Example 4 7 A duplicate of. Example.3 was run.=except'that 15% of Water was-removed instead .ofthe "13%. The product thus obtained was not satisfactory. It was dark-in-color, .stickyan'drubbery and of an entirely different nature tha'n thatproduced in the other examples.

-.'E:rample :5

Using a mixture consisting of 99.5% pentaerythritol (250 .C. M. P.) and0.5'% oftoluenesulionic acid and heating to"200 'C. I obtained a rapid evolution of water. "Theftemperature' was maintained at 210 C. until 13% of water had been driven over. This required about '30 minutes at 210 C.

The final product -contained29.25% ,OH and roduced an E viscosity resininfi "hours.

If more .toluenesulfonic acidis used than the proportions indicated, the evolution of water takes place ata lower temperature (even as low as 180 C.) and the rate .ofievolution, for agiven tempera-ture, may be consi derablyiincreased.

Example/6 19,9.6 parts of pentaerythritol (250C. M. 'P.) were mixed with 0:4 part of p-benzene sulfionic acid dissolved in "10 parts 'of-water'and the mixture heated in the "samemanner as in Example 1.

The mixture startedto melt at 215 C. andbegun to liberate waterat 225 'C. At'240" C.'the rate of water liberation was'satisfa'ctory'andthe mixture was held at this temperatureforfi minutes. 18% of water "wasliberatedby this pr cedure and they hydroxyl content of the product was found to be 33.50 OH.

This product alsojproduced excellent body-tug when ester'rfied as ,describedabove.

Example? Using p-xylene sulfonic acid in substantially the. same manner as "the p benzene sulfonic acid of the previous "example, it wasifoundthat a temperature of 285 C. was required. to effect "the release, of water and that .at/this'temperature a product was obtained "Whic'hwas almost black in color andwasnotuseful inesteri'fication reactions.

The examples givenaboveare confined 'toth'e use of'thearyl sulf'onic acidswithout admixture with any of the oxygen acids of phosphorus.

My work has show-n thatthesuIfonie aci'ds menti'oned' aboveare more satisfactory 'agents ior removing water from the pentaerythritols than are the acids like sulfuric; that is, the water is evolved much more rapidly and the process is more controllable, to give a uniform product. The s-ulfonic acids themselves do not have as great a polymerizing or condensing action upon the dehydration products as do the oxygen acids of sulfur, and therefore are not as prone to cause overpolymerization.

In the following examples are given the details of other modes of applying my invention.

Example 8 595.8 parts of pentaerythritol (M. P. 250 C.) were mixed with 1.2 parts of toluenesulfonic acid, 3 parts of phosphoric acid and parts of water and the mixture heated with stirring. The 10 parts of added water were soon driven out and when the batch reached 215 C. the pentacrythritols give a vigorous evolution of water. This water came out of the pentaerythritol molecule.

The temperature of the reacting mixture was held at 214 to 216 C. for 75 minutes. A portion of the batch was then removed, cooled and pulverized.

A total of 10% of water, based upon the weight of the pentaerythritol, was driven out of the pentaerythritol molecule.

The final product contained 31.33% OH and had a good color. When used to prepare a resin in accordance with the standardized procedure it produced an E viscosity solution in mineral spirits) in 10 hours.

It should be noted that a relatively low temperature Was used in this example. Also, the presence of phosphoric acid caused the mixture to melt at as low a temperature as 180 0., thus improving the ease of operating the process.

Example 9 As stated in Example 5, a portion only of the reaction mixture was removed and tested. The portion remaining in the vessel was heated, with stirring, for minutes additional at 180 C. and a second portion of the liquid contents removed for tests. This second portion contained 29.95% OH and produced an E viscosity resin in 6 /2 hours.

Example 10 The portion of reaction mixture of Example 9 still remaining in the vessel was further heated with stirring for 60 minutes longer, at 180 C. and the product tested as mentioned above. It contained 27.58% OH and produced an E viscosity resin in 5% hours.

All resins produced clear, free flowing 50% solutions in mineral spirits.

Example 11 In a series of tests similar to those given in Examples 9 and 10 except that the reaction temperature for the dehydration step was promptly lowered to 200 C., as soon as the water had started to be released at 215 C. and then held at 200 C., and the mixture otherwise processed as shown in Examples 9 and 10, the products produced were progressively better-bodying agents for resins, but not quite as good as those produced at 215 0., showing that 215 C. is preferable to 200 C.

Example 12 The procedure of any of the Examples 1 to 11 is repeated except that dipentaerythrltol is sub- 6 stituted on a pound for pound basis for the pentaerythritol.

Example 13 The procedure of any of the Examples 1 to 11 is repeated except that tripentaerythritol is substituted on a pound for pound basis for the pentaerythritol.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What I claim is:

1. The method of dehydrating a pentaerythritol selected from the group consisting of pentaerythritol, dipentaerythritol and tripentaerythritol which comprises forming a mixture of the selected pentaerythritol with the sulfonic acid of a monocyclic aromatic hydrocarbon in the proportion of 0.1 to 5 parts for parts of the selected pentaerythritol and heating the mixture at a temperature between that at which water begins to boil out and 270 C., separating water as liberated during the said heating, and discontinuin the heating when the hydroxyl content of the resulting partially dehydrated pentaerythritol falls to a value within the range of 25% to 40% of the weight of the partially dehydrated pentaerythritol.

2. The method described in claim 1, the proportion of the said sulfonic acid being 0.1 to 1 part for 100 parts of the pentaerythritol and the temperature of heating being 215 to 260 C.

3. The method described in claim 1, the said sulfonic acid being toluene sulfonic acid.

4. The method of dehydrating a pentaerythritol selected from the group consisting of pentaerythritol, dipentaerythritol and tripentaerythritol which comprises forming a mixture of the pentaerythritol with the sulfonic acid of a monocyclic aromatic hydrocarbon in the proportion of 0.1 to 5 parts for 100 parts of the pentaerythritol and heating the mixture at a temperature of 180 to 270 C., separating water as liberated during the said heating, and discontinuing the heating when the hydroxyl content of the resulting partially dehydrated pentaerythritol falls to a value within the range 25% to 40% of the weight of the partially dehydrated pentaerythritol.

5. The method of dehydratin a pentaerythritol selected from the group consisting of pentaerythritol, dipentaerythritol and tripentaerythritol which comprises forming a mixture of the selected pentaerythritol with the sulfonic acid of a monocyclic aromatic hydrocarbon in the proportion of 0.1 to 5 parts for 100 parts of the pentaerythritol and an acid selected from the group consisting of phosphoric, phosphorous and metaphosphoric acid in the proportion of 0.1 to 5 parts of the phosphorus-containing acid for 100 parts of the pentaerythritol, heating the mixture at a temperature between that at which Water begins to boil out and 270 C., separating Water as liberated during the said heating, and discontinuing the heating when the hydroxyl content of the resulting partially dehydrated pentaerythritol by analysis falls to 25% to 40%.

JOSEPH A. WYLER.

No references cited. 

